A wireless communications system may generally comprise a set of “subscriber units,” typically subscriber units are the endpoints of a communication path, and a set of “base radios,” (also known as “repeaters”) typically stationary and the intermediaries by which a communication path to a subscriber unit (SU) may be established or maintained. One such type of system is a time division multiple access (TDMA) communication system where the radio medium (or RF frequency) is divided into time slots to carry the communications of the system. Because the communication system carries many communications at one time, a subscriber unit may want to monitor other communications in the system. Scan is a feature that allows a subscriber unit to monitor other communications in the system.
SUs of the wireless communications system utilize a feature termed “scan” where an SU locks on to specific RF frequencies in a preprogrammed list in the SU. The RF frequencies in the scan list may be associated with more than one wireless communications system. For example, an SU may have RF frequencies from the Schaumburg fire department and the Rolling Meadows fire department in its scan list. If the preprogrammed scan list is very long and has many RF frequencies, then the scan feature takes a long time. Further, in the usual case, when many of the RF communications are normally of no interest to the scanning SU, the scanning SU spends a lot of time listening to communications that are of no interest to it. For example, this occurs when an RF frequency is included in the preprogrammed scan list, but the current communication is addressed to a SU or group of SUs that are of no interest to the scanning SU.
Accordingly, there exists a need for scanning a TDMA channel which improves the amount of time that an SU spends scanning.
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